In seismology , several types of surface waves are encountered. Surface waves, in this mechanical sense, are commonly known as either Love waves L waves or Rayleigh waves.
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A seismic wave is a wave that travels through the Earth, often as the result of an earthquake or explosion. Love waves have transverse motion movement is perpendicular to the direction of travel, like light waves , whereas Rayleigh waves have both longitudinal movement parallel to the direction of travel, like sound waves and transverse motion. Seismic waves are studied by seismologists and measured by a seismograph or seismometer. Surface waves span a wide frequency range, and the period of waves that are most damaging is usually 10 seconds or longer.
Surface waves can travel around the globe many times from the largest earthquakes. Surface waves are caused when P waves and S waves come to the surface. Examples are the waves at the surface of water and air ocean surface waves. Another example is internal waves , which can be transmitted along the interface of two water masses of different densities.
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In theory of hearing physiology , the traveling wave TW of Von Bekesy , resulted from an acoustic surface wave of the basilar membrane into the cochlear duct. His theory purported to explain every feature of the auditory sensation owing to these passive mechanical phenomena. Jozef Zwislocki, and later David Kemp , showed that that is unrealistic and that active feedback is necessary.
Ground wave refers to the propagation of radio waves parallel to and adjacent to the surface of the Earth, following the curvature of the Earth. This radiative ground wave is known as the Norton surface wave. Other types of surface wave are the non-radiative Zenneck surface wave     or Zenneck—Sommerfeld surface wave , the trapped surface wave  and the gliding wave. See also Dyakonov surface waves DSW propagating at the interface of transparent materials with different symmetry. Ground propagation works because lower-frequency waves are more strongly diffracted around obstacles due to their long wavelengths , allowing them to follow the Earth's curvature.
Ground waves in radio propagation are not confined to a surface as they are not Zenneck surface waves. The Earth has one refractive index and the atmosphere has another, thus constituting an interface that supports the guided wave's transmission. Ground waves propagate in vertical polarization , with their magnetic field horizontal and electric field close to vertical.
With VLF waves, the ionosphere and earth's surface act as a waveguide.
Conductivity of the surface affects the propagation of ground waves , with more conductive surfaces such as sea water providing better propagation. Since the ground is not a perfect electrical conductor, ground waves are attenuated as they follow the earth's surface. The wavefronts initially are vertical, but the ground, acting as a lossy dielectric, causes the wave to tilt forward as it travels. This directs some of the energy into the earth where it is dissipated,  so that the signal decreases exponentially.
Ground losses become lower at lower frequencies, greatly increasing the coverage of AM stations using the lower end of the band. The VLF and LF frequencies are mostly used for military communications, especially with ships and submarines. The lower the frequency the better the waves penetrate sea water.
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In the development of radio , ground waves were used extensively. Early commercial and professional radio services relied exclusively on long wave , low frequencies and ground-wave propagation. To prevent interference with these services, amateur and experimental transmitters were restricted to the high frequencies HF , felt to be useless since their ground-wave range was limited. Upon discovery of the other propagation modes possible at medium wave and short wave frequencies, the advantages of HF for commercial and military purposes became apparent.
Amateur experimentation was then confined only to authorized frequencies in the range. Mediumwave and shortwave reflect off the ionosphere at night, which is known as skywave. During daylight hours, the lower D layer of the ionosphere forms and absorbs lower frequency energy. This prevents skywave propagation from being very effective on mediumwave frequencies in daylight hours.
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At night, when the D layer dissipates, mediumwave transmissions travel better by skywave. Ground waves do not include ionospheric and tropospheric waves.
The propagation of sound waves through the ground taking advantage of the Earth's ability to more efficiently transmit low frequency is known as audio ground wave AGW. Within microwave field theory , the interface of a dielectric and conductor supports "surface wave transmission". Surface waves have been studied as part of transmission lines and some may be considered as single-wire transmission lines.
Complex, asymmetric curvatures are employed to enhance the performance of optical components while minimizing their weight and size. Kinetics of producing high temperature plasma from nano-particles by means of strong shock waves or high power laser pulses. Nano-crystallites in randomly close-packed media.
Nonlinear dynamics of granular avalanches and flows. Hydrodynamic instabilities at fluid-fluid interfaces , e. You will need to login to see the rest of the lesson. If you do not have a subscription yet, you can join today. Advertisements are not shown when logged in. A must have for high school and university students. This program simulates the orbit of a small planet around a star. You can chose your own starting distance, velocity, and incidence angle. You can then run the orbit simulation in real-time slow or render it, which takes about a minute, and then play it back at a high frame rate , cited: Laser and Plasma Technology: read online Laser and Plasma Technology: 1st:.
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